Northfinding gyro-compasses operate by using gyroscopes to measure the Earth's rate of rotation. Since the Earth's rate of rotation is both a constant and known value, the perceived rate of rotation measured by a gyroscope can be used to determine the amount of angular misalignment between the gyroscopes sensing axis and the axis around which the Earth spins. If a triad of three orthogonally oriented gyroscopes is utilized, each will measure a projection of the Earth's rotation onto the sensing axis of that gyroscope. By utilizing these three projections, the northfinding compass can indicate which direction is north. Gyroscopes typically exhibit some quantity of bias error. That is, they will measure some rate of rotation even when there is no rotation occurring. Gyroscopes that are both accurate and stable (and thus inherently experience relatively little bias error) tend to be large, heavy, and consume large quantities of power. Therefore, they are not well suited for use with miniature, dismounted gyrocompasses that are desirable for applications such as remote targeting applications.
Microelectrical-mechanical (MEMS) gyroscopes represent one technology for producing small, lightweight and low power consuming gyroscope. A good accelerometer may be used in conjunction with the gyroscope, elimination one degree of freedom by pointing the gyroscope's sense axis towards the Earth's center. Dithering techniques have also been developed to mitigate bias error in these MEMS devices and address the other degree of freedom. That is, the MEMS gyroscopes are mechanically oscillated at a set modulation frequency along their sensing axis with respect to the estimated direction of North. This motion results in the MEMS gyroscope producing a rotation rate output signal that is modulated in time. By demodulating that signal, the bias error is removed and a measurement of the Earth's rotation rate can be obtained. However, implementation of this dithering involves mounting each MEMS gyroscope on a platform that includes rotating stages. Thus mechanical dithering of the MEMS gyroscopes introduces additional moving parts that are subject to wear-and-tear, mechanical failure, and varying performance characteristics over time.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for optically dithered atomic gyro-compasses.